Glass deterioration, also known as glass disease, happens when alkaline components leach out to the surface of the glass. It’s believed to have two contributing factors: unstable composition of the glass, and incorrect relative humidity. This problem is particularly difficult to address in composite items decorated with small, tightly bound glass beads and may also incorporate other materials. Eventually, the affected glass will crack and crumble, causing the loss of culturally significant beaded designs.
In 2015, conservation staff at the Field Museum began a survey of Native North American beadwork items from the Plains region to identify beaded items suffering from glass deterioration. Beads were tested for stability by pressing dampened pH strips to the surface following O’Hern and McHugh. The measured surface pH was used to give a treatment priority to each item. Items with pH of 8 or above were included in the next phase, the bead stabilization project, which began in 2021. Approximately 2,000 catalog numbers were surveyed, and 786 were ultimately included in the stabilization project.
Our method for trying to slow down the glass deterioration is microclimate storage at stable relative humidity (RH) in the low 40 %RH range. All items are documented through photography and condition reports and then housed in stable relative humidity. Smaller items are stored in gasketed metal cabinets with conditioned silica gel. For larger items, a custom Escal barrier film enclosure is created for each item, with a packet containing silica gel buffer and a humidity indicator card. Given the density of packing of the items in the cabinets and Escal enclosures, it was found to be important to acclimate the items to the correct RH prior to storage.
Covid-19 and the large volume of material restricted the scope of collaboration with Native Communities associated with the items being treated and re-housed. Nonetheless, we were able to engage the Native American community through a three-day workshop, hosted at the museum for people from Native American Plains communities who have a role in caring for beaded items. This workshop was an opportunity to share trusted collection care resources, show how the Field Museum cares for beadwork, and provide an opportunity for hands-on practice cleaning beads and creating archival housings.
Over the course of the project, we have encountered many challenges, including a slow start due to Covid-19 restrictions, schedule delays, multiple staff departures, competing departmental priorities, and more. In this paper we discuss the survey methodology and results, the rationale and practical implementation of our relative humidity stabilization methods, and our strategies for overcoming these challenges and reconciling our conflicting priorities.
The documentation, treatment, and rehousing of the items in the bead stabilization project, as well as the workshop, were made possible in part by the Institute of Museum and Library Services grant number MA-245371-OMS-20.
